1. Field of the Invention
The present invention relates to a numerical control method and a numerical control system used for the control of various types of PTP (point to point) operations such as robot control, temperature control, camera focus control, slide control of a CD player, video disk, and the like, and DC point control of electrical circuits. More particularly, it relates to a numerical control method and numerical control system which enable free setting of a pattern of acceleration and deceleration free from the amount of movement or the time of movement.
2. Description of the Related Art
In general, in a servo control circuit, there is known a method for converting information on the phase and speed of a controlled object to a pattern, storing the same in advance in a memory, and later reading out the information in accordance with a target point to control the object at different points of time. In this case, the acceleration curve and deceleration curve are tinkered with so that the controlled object will be operated smoothly and within the desired time.
For example, the most general pattern of acceleration and deceleration is the triangular pattern shown in FIG. 1A, but since the acceleration jumps at three locations: the starting point of movement, the peak point, and the target point, it suffers form the disadvantage that a shock is easily given to the mechanical system. Further, this cannot be said to be optimal as the input to a servo control circuit.
Therefore, as shown in FIG. 1B, a proposal has been made of a pattern of acceleration and deceleration which provides a constant speed portion F as a stopping measure immediately before the target point. Even with this pattern of acceleration and deceleration, the jumps in acceleration at the starting point of movement and the peak point in the transition from acceleration to deceleration are not eliminated, so it also suffers from the disadvantage that the shock to the mechanical system cannot be completely resolved. Further, the disadvantage that the input is not the optimal one for a servo control system similarly remains.
On the other hand, to achieve a smooth operation at the time of acceleration and deceleration, a method has been proposed of storing in advance in a read-only-memory (ROM) the smooth pattern of acceleration and deceleration as shown in FIG. 2A. By this technique, problems in overshooting and precision of stopping are remarkably eliminated. However, the acceleration and deceleration times are made constant, so if the amount of movement is increased, the acceleration and deceleration curve also grows higher as shown in FIG. 2B and the problems in the precision of stopping at the time of a stop and shock to the mechanical system reappear. Further, it suffers from the disadvantage that the form of the acceleration and deceleration cannot be freely changed.
To overcome the above disadvantages, as shown in FIG. 3, a method has been proposed of classifying the amount of movements into large, medium, and small movement and storing in advance in a ROM patterns of acceleration and deceleration with acceleration times and deceleration times suitable for each of the same. The disadvantage nonetheless remains in that this results in a massive required memory capacity and further unnatural characteristics of the amount of movement and movement time, so is not preferable in terms of control. Further, it was not possible to freely change the acceleration and deceleration by this technique.